Light emitting diode display for electronic timepiece

ABSTRACT

There is disclosed a light emitting diode timepiee display in which the output of the light emitting diode display is controlled with respect to ambient lighting conditions so as to provide the maximum amount of contrast with a minimum amount of power consumption. The contrast between the light emitted by the light emitting diodes and the ambient light in the immediate vicinity of the timepiece is enhanced by the use of absorption type filters, truncated pyramid type apertures in the display cover plate and a control circuit which adjusts the intensity of the output of the light emitting diodes to the ambient light conditions. Thereis further provided a series of solar cells on the face of the display, which recharge the timepiece batteries during ultra-high ambient light conditions and which supply additional power to the light emitting diodes during high ambient lighting conditions so as to increase the output of the light emitting diodes. This enhances the contrast of the diodes during high ambient lighting conditions while at the same time providing an additional source of power in parallel with that of the timepiece battery so as to increase the effective lifetime of the battery. Power distribution between the solar cells and the battery is controlled by the aforementioned control circuit. In addition, the control circuit varies the power available to the light emitting diodes such that in low ambient lighting conditions a lesser amount of power is delivered to the light emitting diodes while in high ambient lighting conditions, a larger amount of power is delivered to the diodes. In this manner the aforementioned contrast is kept constant and at that level which corresponds to the minimum level necessary for ready visibility. In addition, several structural embodiments are shown, all of which contribute to the enhancement of the light output of the light emitting diodes, the enhancement of display contrast, low power consumption, ease of fabrication, and mechanical stability of the final product.

[ Sept, 1111, 1973 LlGHT EMlTTlNG DllOlDE DISPLAY FOR ELECTRONICTIMEPIECE [75] Inventors: Ronald R. Burgess, Phoenix; Michael G.Coleman, Tempe; Lawrence A. Grenon, Phoenix, all of Ariz.

[73] Assignee: Motorola, lnc., Franklin Park, Ill.

[22] Filed: May 17, 1971 [21] Appl. No.: 143,837

[52] US. Cl. 58/50 R, 58/127 R, 350/267 [51] lot. Cl. G04c 3/00, G04b19/06 [58] Field of Search 58/23 R, 23 A, 23 BA, 58/23 C, 50 R, 127;350/267; 340/309.4

[56] References Cited UNlTED STATES PATENTS 3,672,155 6/1972 Bergey etal. 58/50 R 3,630,015 12/1971 Lehovecn 58/50 R 3,509,715 5/1971 DeKoster58/50 R Primary Examiner-Richard B. Wilkinson Assistant Examiner-EdithC. Simmons Jackmon Attorney-Mueller & Aichele [57] ABSTRACT There isdisclosed a light emitting diode timepiee display in which the output ofthe light emitting diode display is controlled with respect to ambientlighting conditions so as to provide the maximum amount of contrast witha minimum amount of power consumption. The contrast between the lightemitted by the light emitting diodes and the ambient light in theimmediate vicinity of the timepiece is enhanced by the use of absorptiontype filters, truncated pyramid type apertures in the display coverplate and a control circuit which adjusts the intensity of the output ofthe light emitting diodes to the ambient light conditions. Thereisfurther provided a series of solar cells on the face of the display,which recharge the timepiece batteries during ultra-high ambient lightconditions and which supply additional power to the light emittingdiodes during high ambient lighting conditions so as to increase theoutput of the light emitting diodes. This enhances the contrast of thediodes during high ambient lighting conditions while at the same timeproviding an additional source of power in parallel with that of thetimepiece battery so as to increase the effective lifetime of thebattery. Power distribution between the solar cells and the battery iscontrolled by the aforementioned control circuit. In addition, thecontrol circuit varies the power available to the light emitting diodessuch that in low ambient lighting conditions a lesser amount of power isdelivered to the light emitting diodes while in high ambient lightingconditions, a larger amount of power is delivered to the diodes. in thismanner the aforementioned contrast is kept constant and at that levelwhich corresponds to the minimum level necessary for ready visibility.In addition, several structural embodiments are' shown, all of whichcontribute to the enhancement of the light output of the light emittingdiodes, the enhancement of display contrast, low power consumption, easeof fabrication, andmechanical stability of the final product.

27 Claims, 27 Drawing Figures SOLAR CELLS, 35

PHOTO DETECTOR,34

FACE PLATE 36 INSULATION 32 msumnomes VF! T R g6 37 39 LOGIC /i /s L E,3l

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FACE PLATE INSULATION 32 |N8ULATION,33 I I '36 3? 39 38 37 3e 26 6 LOGIC('5 u w I l I l I 23 I 25 I I I I I 2| x l LEDS 4o POWER CONTROL PowERTO LOGIC CKT FROM SOLAR CELLS I o H BATTERY,4I

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I I I 2 INVENTOR Arrr's.

PMENIEB SEP] 1 I975 SHEEI 2 0f 9 NVENTOR E. Burgess Michael 6. ColemanLawrence A. Grenon WM/M PATENTEDSEPY 1 I915 3,757. 51 1 SHEET 3 [IF 9SOLAR CELLS, 35

CONTROL CKT,4O LOGIC CKT.25

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INVENTOR Ronald R. Burgess BY Michael 61 Co/eman IOO SHEEI t 0F 9 WAJPAIENTEDSEPI a 1913 Fig 5b N l\ \i\ W INVENTOR Ronald R. Burgess ATTY'SMichael 6. Coleman Lawrence A. Grenon PAIENTEDSEPI Hm 3.757.511

SHEET 5 0F 9 I08 I07 I08 I00 IOI I00 l I00 I04 110 I08 I08 no I04 101PHOTO :45 LED SOLAR CELL DET SOLAR CELL LED m w g POLY Si, ||2 1 LOGIC IINVENTOR WWKM ATTY'S PAIENIEDSEPI 1 I913 3.757. 51 1 I SHEET 6 BF 9 ANREFLECTION FILTER, 3|

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INSULATING SUBSTRATE,2I

INSULATING S U BST RATE, 2|

I INVENTOR Rona/0' A. Burgess BY Michael 6. Co/em an L awren ca 4.Grenon M QMM/ PAIENIEUSEPHIBH 3,757,511

SHLU 7 0F 9 INVENTOR Rona/d R.BUFQSS BY Michael 6 Coleman Lawrence A.Gre'non WMMMM PATENTED SEPT I I975 SHEET 9 UP 9 X /-PHOTO DETECTOR, 34

I i I 40 25 2? 43 SECONDARY POWER SOURCE,42

IT TX I POWER CONTROL CKT.

DISTRIBUTION LEVEL MIN a OVER-RIDE LED 23 SWITCH, 200 W \PRIMARYBATTERY, 4|

I NVE NTOR.

Ronald R. Burgess Michael 6. Coleman Lawrence A. Grenon WWW/ ATTY'S.

l LHGHT EMTTTHNG DlUlDlE DTSIPLAY FOR ELECTRONTC TllMEPlECE BACKGROUNDOF THE INVENTION This invention relates to electro-optical displays forelectronic timepieces and more particularly to horologic displays usinglight emitting diodes in configurations which conserve power and thusextend battery lifetime for batteries utilized in providing power forthe electronic timepiece.

While battery powered electronic watches utilizing classical electricmotors in conjunction with mechanical drive mechanisms are commonplace,these watches suffer from dust and other particulate matter whichinvades the mechanical actuating mechanism and the mechanical displayportions of the watch. The obvious problems with an electro-mechanicalwatch have been recognized for some time with respect to the amount ofservicing necessary and the wear on the moving parts. Additionally,watches utilizing hands" even when coated with luminous radioactivematerial are not easily read in low light ambient conditions.

Although all-electronic watches utilizing light emitting diodes havebeen made, they are in general unsatisfactory due to the powerconsumption of the light emitting diodes. This high power consumptionprevents continuous readout of the timepiece because continu ous readoutruns battery powered watches down in a matter of weeks. Thus, electronicwatches utilizing light emitting diodes have displays which areactivated only a certain number of times per day in an effort to extendthe lifetime of the battery used therewith. This is not onlyinconvenient but annoying to the user. The subject invention permits theuse of a light emitting diode display on a wrist watch in which allpower saving parameters are maximized so that the watch may be read outcontinuously for a reasonable period of time (a year or more) withoutreplacing the watch battery. The battery drain during the continuousreadout is kept to a minimum by the use of several light enhancementtechniques, power supplementing techniques, and light emission controlcircuitry.

Specifically, in one embodiment in the cover plate over each of thelight emitting diodes utilized is a truncated pyramid type aperturepositioned over the light emitting diode therebeneath having sidewallswhich are inclined. Secondly, overtop of each light emitting diode is anarrow band-pass filter which either absorbs white light and transmitsonly the light emitted from the diode or which is a circularly polarizedfilter which attenuates light passing twice through it. This enhancesthe contrast of the display which refers to the difference in intensityof the light at the surface of the diode as compared with the surfacebrightness of that portion of the watch face around the diode. Byenhancing the contrast, power consumption for acceptable visibility canbe significantly lowered. The apertured watch cover plate in thepreferred embodiment is made from silicon having a [100]crystallographic orientation which permits easy aperture formation. Thisparticular crystallographic orientation provides for the aforementionedtruncated pyramid type apertures when silicon of this crystallographicorientation is etched through a square mask with a potassium hydroxideetching solution.

At this point it should be pointed out that a cover for any type lightemitting diode display can be made hav- 2 ing apertures with inclinedsidewalls by utilizing a crystalline material which is etchedpreferentially in a given direction by a particular etchant. The lightenhancement function of the inclined sidewalls with respect to lightemitted by light emitting diodes is described hereinafter.

The contrast enhancement afforded by the afore mentioned apertures andthe narrow band-pass filter has utility both when power consumption is aproblem and when an unlimited power supply is available for theall-electronic watch or clock. Thus, the light emitting diode displaydescribed herein may be utilized in automobiles, aircraft, and innon-mobile applications for contrast enhancement purposes where powerconsumption is not a problem.

In addition to contrast enhancement, the subject technique provides forcontrast compensation to minimize power consumption. Where powerconsumption is a problem, as in battery operated wrist watches, thesubject device includes an ambient light sensor and a control circuitwhich adjusts the output of the light emitting diodes such that in highambient light conditions the light emitting diodes have a high output,while in low ambient lighting conditions the output of the lightemitting diodes is limited by reducing the power thereto. It will beappreciated that in low ambient light conditions, such as at night, therequisite amount of contrast can be obtained with lower outputs from thelight emitting diodes. Concomitantly in high ambient lightingconditions, the output of the diodes must be increased so as to providefor the aforementioned contrast. Thus the contrast is kept substantiallyconstant and in so doing power consumption by the light emitting diodedisplay is minimized.

In addition to the ambient light sensing and power control, the subjectdisplay is provided with a secondary power source in the form of solarcells. These solar cells provide two functions in high ambient lightconditions. The first function is to recharge the battery for thedisplay. Additionally and simultaneously the solar cells increase thepower available to the light emitting diodes during high ambient lightconditions so as to increase the output of the light emitting diodestherefore providing an acceptable contrast between the light emitted bythe diodes and the ambient light reflected at the surface of thedisplay. The secondary power source is not limited to the preferredsolar cells and may in fact be a secondary battery which is switchedinto the circuit during high ambient lighting conditions so as toprovide the additional power to the light emitting diodes. The powerdistribution from the secondary power source and the primary powersource are controlled by the aforementioned control circuit.

There are also disclosed several fabriction techniques for making thecompleted display. The first of these techniques is a monolithicfabriction technique which results in reliability, shock resistance andphysical thinness of a completed timepiece. A somewhat less expensivefabrication technique involves a hybrid layered structure withsemiconductor support members and display covers. A third fabricationtechnique involves the use of a conventional printed circuit board,discrete devices and either a toroidal plastic cover or a silicon faceplate with the aforementioned apertures therethrough. In addition, theaforementioned silicon cover plates provides a substrate into which canbe grown or diffused the aforementioned solar cells and the ambientlight sensing device, thus providing for a mechanically stablestructure.

While the following discussion will be limited to electronic timepiecedisplays, the invention described herein applies to an electro-opticaldisplay utilizing light emitting diodes in which contrast is to bemaximized and power consumption minimized.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide an improved electronic timepiece in which the display for thetimepiece includes light emitting diodes in a high contrastconfiguration.

It is another object of this invention to provide an improved electronictimepiece utilizing a light emitting diode display in which the powerconsumption of the light emitting diodes is minimized.

It is a still further object of the invention to provide an improvedelectronic timepiece utilizing a light emitting diode display in whichwatch face contrast is enhanced by the use of narrow band-pass filtermaterial.

It is a still further object of this invention to provide an improvedelectric timepiece utilizing a light emitting diode display in whichdisplay contrast is enhanced by the use of a cover plate on top of thelight emitting diodes having an inclined sidewall type aperture at eachdiode and through which the emission of each diode passes.

It is a still further object of this invention to provide an improvedelectric timepiece utilizing a light emitting diode display in whichpower consumption of the display is minimized by sensing ambientlighting conditions and adjusting the output of the light emittingdiodes so as to obtain the minimum amount diode output for an acceptablecontrast.

It is a still further object of this invention to provide an improvedelectronic timepiece utilizing a light emitting diode display in whichthe ambient lighting condition is sensed and in which the primary powersupply is augmented by a secondary power supply during high ambientlighting cnditions so as to increase the output of the light emittingdiodes during the occurrence of a high ambient lighting condition.

It is yet another object of this invention to provide an improvedelectronic timepiece having a light emitting diode display in which thetimepiece is supplied with a secondary power source including a numberof serially connected solar cells whose output is connected in parallelwith the primary source whenever the ambient lighting condition for thetimepiece is high, the solar cells providing a recharging function forthe primary power source as well as a power enhancing function for thelight emitting diodes during high ambient lighting conditions.

It is yet another object of this invention to provide an improvedelectronic timepiece utilizing a light emitting diode display in whichboth the display and logic portions of the timepiece are fabricated inmonolithic form.

It is a still further object of this invention to provide an improvedelectronic timepiece having a light emitting diode display in which thedisplay portion of the timepiece is fabricated in a layeredconfiguration with one of the layers being a substrate for the lightemitting diodes and the second layer serving as a cover for the display,as a narrow band-pass filter, and as a support for solar cells and anambient light sensor.

It is yet a still further object of this invention to provide a coverfor an electro-optical display in which the apertures in the cover haveinclined sidewalls formed by etching a crystalline material in apreferential direc tion.

Other objects of this invention will be better understood upon readingthe following description in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cutaway drawing ofthe light emitting diode display including the placement of solar cellsand a photodetector on top of the face plate with interconnectionsthrough the face plate and through the support of the light emittingdiodes to a power control circuit whose function is to both alter thepower to the light emitting diodes and to distribute the power from thetimepiece battery and the solar cells so as to take maximum advantage ofthe light energy impinging on the face plate of the timepiece.

FIG. 2 is a block diagram showing primary and secondary power sourcescoupled to a power control circuit to which is also coupled an ambientlight sensor, the output of the power control circuit being coupled to alogic circuit which then drives the light emitting diode display.

FIG. 3 is a cutaway diagram showing the solar cells and the ambientlight sensing device diffused into a face plate made of a semiconductivematerial.

FIG. 4 is a diagram of a light emitting diode in which the lightgenerated emanates from the top surface of the diode.

FIG. 5 is a diagram of a light emitting diode in which light emerges inboth a horizontal and a vertical direction.

FIGS. 6, 7 and 8 show inclined wall and straight wall apertures throughwhich the light from light emitting diodes passes, indicating theadvantages of each configuration.

FIG. 9 indicates a light emitting diode timepiece display in which thereadout is in alpha-numeric form.

FIG. 10 is a diagram in partial cross section of a light emitting diodedisplay including solar cells and a photodetector mounted on top of asubstrate, showing a toroidal cover for the diodes. There is also shownthe embedding of the control circuit and logic circuit in the substratewith a battery immediately adjacent the logic circuit.

FIG. 11 is a graph showing current output of solar cells as a functionof the brightness of the ambient light.

FIG. 12 is a graph relating the current driving light emitting diode tothe brightness of the output of the diode.

FIGS. l3a-l3i show the fabrication of a monolithic timepiece lightemitting diode display.

FIG. 14 is a partial cutaway drawing showing the construction of a lightemitting diode display for a timepiece indicating a two layerconfiguration in which the top or cover layer includes a face platehaving apertures therethrough and a narrow band-pass filter within eachaperture in the face plate.

FIG. 15 shows a hybrid configuration for a light emitting diode displayutilized in timepieces in which the narrow band-pass filter is in theform of a hemi-toroidal cover.

FIGS. 16 and 17 are top views of the subject display showing 72 and 84diode arrays respectively for telling time by the second, minute, hourand in the case of FIG. t7, the half hour.

FIG. w is a block diagram showing one possible logic circuit to drivethe display, and

FIG. I9 is a block diagram showing a circuit which permits the displayto be turned off under complete darkness conditions, also showing anover-ride switch.

BRIEF DESCRIPTION OF THE INVENTION There is disclosed a light emittingdiode electronic timepiece display in which the outputs of the lightemitting diodes are controlled with respect to ambient lightingconditions so as to provide the maximum amount of contrast with aminimum amount of power consumption. The contrast between the lightemitted by the light emitting diodes and the ambient light in theimmediate vicinity of the display is enhanced by the use of narrowband-pass filters, inclined sidewall type apertures in the display coverand a control circuit which adjusts the intensity of the output of thelight emitting diodes to the ambient lighting conditions so as tomaintain a constant contrast between the display and ambient lightreflected from the surface of the display. There is further provided, inone embodiment, a series of solar cells on the face of the display,which recharge the timepiece batteries during ultra-high ambient lightconditions and which supply additional power to the light emittingdiodes during high ambient light conditions so as to increase the outputof the light emitting diodes. This enhances the contrast of the diodesduring high ambient light conditions while at the same time providing anadditional source of power in parallel with that of the timepiecebattery so as to increase the effective lifetime of the battery. Powerdistribution between the solar cells and the battery is controlled bythe aforementioned control circuit. In addition, the control circuitadjusts the power available to the light emitting diodes such that inlow ambient lighting conditions a lesser amount of power is delivered tothe light emitting diodes while in high ambient lighting conditions, alarger amount of power is delivered to the diodes such that theaforementioned contrast is kept constant and at the level whichcorresponds to the minimum level necessary for acceptable visibility ofthe display. In addition, several structural embodiments are shown, allof which contributing in some measure to the enhancement of the lightoutput of the light emitting diodes, the enhancement of displaycontrast, low power consumption, ease of fabrication, and mechanicalstability of the final product.

DETAILED DESCRIPTION OF THE INVENTION tant with these numbers of diodesis the power consumption which makes continuous readout of these devicesimpractical when the timepieces are to be powered by portableself-contained batteries. There is, however, another way of displayingtime, described in detail in connection with FIGS. M and I7, involvingthe use of a plurality. of concentric circles. If two concentric circlesare used to represent the time of day having 12 and individual lightemitting diodes respectively, the time is read out from this display bysimultaneously reading out one diode from the ring of I2 indicating thehour; and two diodes from the ring of 60 representing numbers andseconds respectively. Alternatively, an additional 12 diodes l2 diodescan be used in the ring already containing 12 diodes to represent halfhour intervals. These additional diodes are useful in resolvingambiguities resulting from readouts near the hour change. Thus, at anyone time no more than four diodes are lit as compared with as many as 87diodes in an unstrobed alpha-numeric matrixed display. The logicnecessary to power or drive the subject display is described inconnection with FIG. 18 and consists of a frequency standard, variouselectronic countdown circuits, decoding circuits and driving circuits.

One prior art example of display utilizing light emitting elements toindicate the time of day is shown in the U.S. Pat. to R. D. Anderson,No. 3,455,152 issued July 15, 1969. Both the electronic clock shown inthe Anderson patent and the variety of alpha-numeric electronic clocksand wrist watches, known to the prior art, suffer from theaforementioned power consumption to such degree that they cannot beutilized in wrist watch form with batteries conventionally available forany length of time in a continuous readout mode.

Th electronic timepiece to be described herein is capable of being readout continuously for a year without changing the primary battery in thesystem. While logic circuits have been devised which utilize on theorder of 5 microamps of current in the mode in which the subject displayis driven, the subject display draws only an additional 10 microamps inaddition to the 5 microamps of the logic circuit. This permits theoperation of the subject timepiece on a 3 volt battery for at least oneyear when either 72 or 84 diode elements are utilized in theconfiguration in which either 3 or 4 elements are lit at one time. Inthis manner a continuous readout is obtainable over a period of longerthan one year.

There are two mechanisms which decrease the power consumption of thedisplay. The first utilizes the concept that for a given ambientlighting condition there is a minimum readable output from the lightemitting diodes. In low ambient lighting conditions the output of thediodes need be considerably less than in high ambient lightingconditions. In the subject display there is provided an ambient lightsensing device in combination with a power control circuit which adjuststhe power to the light emitting diodes of the display so as to minimizethe power consumption the th diodes. Secondly, advantage is taken of theenergy contained in the light impinging on th surface of the timepiece.To this end the timepiece is provided with a series of solar cells whichfunction either to increase the power to the light emitting diodesduring high ambient lighting conditions or to recharge the primarybattery for the timepiece. The power consumption of these diodes isfurther reduced by the use of narrow band-pass filter over the lightemitting diodes. In addition the timepiece cover has apertures havinginclined sidewalls therethrough, which in one configuration are in theform of truncated pyramids. These two structural components increase thecontrast between the diodes and the surfaces surrounding them so as topermit a decrease in the output from the diodes necessary to maintain agiven contrast.

Referring now to FIG. 1, a light emitting diode timepiece display isshown being comprised of a substrate 21 and a cover plate 22. At theperiphery of the substrate 21 are mounted a plurality of light emittingdiodes 23 on top of metallization 24 which is configured in a mannercompatible with the timepiece logic 25 shown centrally located andmounted on the substrate 21. A simplified logic is shown in FIG. 18 tobe described hereinafter. The metallization 24 provides contact to oneelectrode of the light emitting diodes 23. Further metallizaiton strips26 connect various of the opposite electrodes of the light emittingdiodes 23 to the logic 25. As can be seen from this figure, a coverplate 22 is provided with a multiplicity of apertures 30 which arepositioned over respective diodes 23. Within or behind these aperturesare provided the aforementioned filters 31. Mounted on top of the coverplate 22 are solar cells which are provided with contact metaliizationlayers and structures 36 and 37 which protrude through the cover and thesubstrate so as to connect the solar cells to the power control circuitshown at 40. Member 36 is isolated from the solar cell by isolation 33.Also mounted on top of the cover 22 is an ambient light sensor,designated photodetector 34 having contacts thereto labelled 38 and 39.These contacts also protrude through the substrate 21 to connect thephotodetector to the power control circuit 40. Battery 41 which is theprimary source of energy for the timepiece 20 is also connected to thepower control circuit 40.

The light emitting diodes 23 are of a conventional configuration and,depending on the color of the output desired, can be fabricated fromgallium arsenide phosphide, gallium phosphide, gallium arsenide coatedwith phosphors, gallium aluminum arsenide, and indium gallium phosphide.Indeed, any light emitting diode material may be utilized if the lightemitted is in the visible range. Gallium arsenide with phosphorsfunction such that the phosphor up converts the infrared radiationgenerated to visible light.

The substrate 21 on which the light emitting diodes 23 are mounted canbe of any insulating material. In particular, it may be of a printedcircuit board configuration with the metallization being copper, thecopper being plated with gold to prevent corrosion. The substrate 21 canalso be made of a ceramic material or indeed of a semiconductor materialwith isolated light emitting diodes grown or embedded therein. Thisconfiguration is shown in connection with FIGS. l3a-l3i to be discussedhereinafter. It will be appreciated that if the substrate 21 is of asemiconductive material, the only requirement is that the diodes beelectrically isolated, one from another. This can be done either bydielectric isolation or junction isolation such that the substrate 21does not have to be an insulator. Obviously, the diodes 23 and themetallization 24 and 26 can be made to adhere to almost any type ofsubstrate.

Although the diodes 23 are shown mounted on a continuous back contactmetallization layer 24, the back contact to the diodes may be made inany convenient manner compatible with the logic 25. This may involve theuse of segmented families as shown in the aforementioned Andersonpatent. In general, the metallization over the substrate 21 is eitherstandard silver or gold metallization such as would adhere to ceramics,is standard copper on conventional circuit boards which is latter platedwith gold, or is titanium-molybdenum- 8 gold, titanium-nickel-gold, ortitanium-nichromealuminum.

The cover plate 22 can be in general to be an opaque ceramic, plastic orglass having a pleasing appearance. The cover plate can also be metallicif appropriate isulation is provided for the solar cells, thephotodetector and the leads therefrom. Additionally, the cover plate 22can be made from a semiconductor material which is etched in apreferential direction such as silicon. If a silicon cover plate 22having a crystallographic orientation is utilized, the apertures 30having inclined sidewalls can be easily fabricated. These apertures takeon a truncated pyramid type form, as shown in FIG. 1, by providing anetch mask over the cover plate 22 having square apertures therethrough.When hot potassium hydroxide is utilized to etch through this particulartype of silicon, the truncated apertures, whose utility will bedescribed hereinafter, are readily formed.

The inclined sidewall structure is useful in display covers other thanthose utilized with watches. In fact, there is a light enhancementcharacteristic associated with inclined sidewalls for anyelectro-optical display. These sidewall inclinations are easily formedin crystalline material, which due to its crystallographic orientationis etched in a preferential direction. This is called anisotropicetching. Thus for [100] silicon, the crystal is etched by potassiumhydroxide only along one plane. This preferential etching gives asidewall inclination with the vertical at an angle c5 of 54. Othercrystals in other crystallographic orientations also are preferentiallyetchable. Thus inclined sidewall apertures can be formed byphotolithographic techniques over an entire array of light emittingdiodes without grinding or cutting operations. The light enhancementcharacteristics of these inclined sidewall apertures with respect tolight emitting diodes will be discussed in connection with FIGS. 6, 7and 8.

The solar cells 35 are typically fabricated from gallium arsenide,silicon and germanium. However, high output solar cells are available inmost semiconductor materials. The output of these solar cells is ingeneral less than the maximum theoretical output and is roughly equal tothe band gap of the solar cell material. At present, the optimum outputvoltage for a silicon solar cell is approximately 0.6 volts at the powerdrains involved. If the timepiece is to be designed with a 3.0 voltprimary battery or even a 1.5 volt primary battery, a number of solarcells connected in series are preferred. The number of solar cells to beconnected in series is dictated by the total voltage output desired. Ingeneral and in the configuration shown, it is desirable to have a totaloutput voltage from the solar cells in excess of that of the primarybattery so that the solar cells can be connected in parallel with theprimary battery either to recharge it or to provide additional power tothe light emitting diodes. Provisions must be made in the controlcircuit 40 to prevent the solar 'cells from loading the battery andtherefore causing additional drain thereon. If the output of the solarcells is less than that of the primary battery, a DC to DC converteroperating at very high efficiency is necessary to transfer the powerfrom the solar cells to the battery.

With respect to the photodetector 34, the most common photodetector ismade of cadmium sulfide. This detector can, however, be any type ofphototransistor, photodiode or photoresistor whose characteristics varywith the amount of light impinging thereon. There is no attempt made atthis point to match the characteristics of the photodetector with thoseof the solar cells although there will he obviously a correlationbetween the output of the solar cells 35 and the internalcharacteristics of the photodetector M with respect to the ambientlighting condition described hereinbefore.

As shown in lFlG. 2, the power control circuit in conjunction with thephotodetector 34, the primary battery di and the secondary power sourceshown diagrammatically at 42, serves at least three functions.

In connection with the photodetector 34, it is one function of the powercontrol circuit dill to vary the amount of power delivered to the logiccircuit 25 and thus to the light emitting diodes represented here by asingle diode 23. The power driving the light emitting diode 23 iscontrolled by controlling the current to the light emitting diode. Thisis accomplished by sensing the ambient lighting condition shown by thearrows d3 such that the current delivered is a direction function of theintensity of the light detected at the photodetector 3 3. Thus thehigher the ambient lighting condition the more power delivered to thelight emitting diode. The amount of current reduction dictated by a lowambient lighting condition, suchas occurs at night, is related to theaforementioned contrast desired. In general, the contrast is thedifference between the surface brightness of the light emitting diode ascompared to the surface brightness of the area immediately surroundingthe diode in the display. After having ascertained a certain desirablebut minimum contrast, the power control circuit 40 maintains thiscontrast during all lighting conditions. The effect of the maintenanceof this contrast is to reduce the power to the light emitting diodesduring low ambient lighting conditions thus conserving power.

The second function of the power control circuit is to regulate thedistribution of the power from the primary battery 41 and the secondarypower source 42 which in this case is the solar cell 35. Thisdistribution regulation may take three alternate forms. The first ismerely a switching function. When the ambient light, as detected by thephotodetector 3d, exceeds a predetermined threshold, power from thesolar cell 35 is switched directly to the logic circuit 25 and thus tothe light emitting diode 23, while at the same time eliminating theprimary battery 41 from the circuit. This conserves the primary batterypower by substituting the power generated by the solar cell 35.Secondaly, with the use of a blocking diode M and the combined solarcell output 35 being greater during high ambient lighting conditionsthan that of the primary battery 41, the output of the solar cell may beconnected in parallel across the primary battery. This serves in and ofitself two functions. The first is to recharge the battery during highambient light conditions and the second is to provide additional powerto the light emitting diode during these high ambient lightingconditions. The blocking diode dd prevents the solar cell 34 fromdraining or providing a load for the battery 41 during low ambientlighting conditions.

Thirdly, more sophisticated power control circuits can be devised forthe power control circuits 40 such that a given amount of power from thesolar cell 35 diverted for use in powering the light emitting diodewhile another portion of this power is diverted to charge the primarybattery All.

Jill) Thus the functions of the power control circuit d ll arethreefold: the first being to control the amount of power to the lightemitting diode; the second being the supplementing of the powerderivable from the primary battery by a secondary power source; and thethird being the recharging of the primary battery when the secondarypower source is in the form of a solar cell. It will be appreciated thatcontrol circuits to provide each of the aforementioned functions areknown and may be obtained in integrated circuit form.

in the configuration shown in FIGLT only the outermost ring of diodeelements is shown. As will be shown in connection with FIGS. 16 and 117,in the preferred embodiment there are two concentric rings of elementswith the inner ring denoting the hour, and outer ring denoting theminutes and seconds. At any given time three diodes are lit thusconserving power over alphanumeric displays. However, if the outer ringof diodes were to run in continuous operation not only would there bemore of a power drain but also there might be a hypnotic effect. If thisdisplay were to be used in a car there would of necessity be a need forsome way of interrupting the signals to outer ring of diodes containingthe information for the seconds display, during period when thedetermination of time to the second is unnecessary. The subject displayis provided with means, shown by switch 27, to cause such a signalinterruption. The system can be arranged such that by pushing a buttonon the timepiece either seconds can be read out until the button isreleased or seconds can be read out until the button is again pushed.However, the configurations of the invention shown herein do not dependon intermittent readout of seconds for their longevity. With thecontrast enhancing structures and the power control circuitry describedherein, assuming three or four diodes are read out at a time, theprimary battery for the timepiece will last for more than one year.

Referring to FIG. 3, the solar cells 35 and the photodetector 34 areshown in monolithic form embedded in the cover plate 22. In this caseboth the solar cells and the photodetector are isolated by dieletricisolation 50 since it will be appreciated that junction isolation is notsufficient, to permit proper operation of the solar cells and thedetector. Also shown in FIG. 3 are a variety of contacts resting on topof the dielectric isolation layer 50. It is in this configuration thatconnections between the solar cells and the photodetector and the restof the watch assembly can be most easily made. In this configuration aportion of the watch case (shown in connection with FIG. 13) overlapsthe contact pads 51. This watch cover or case has correspondingmetallization layers running on the inside of the watch case down aroundthe edge of the cover plate 22 and terminating at the respective-circuitelements, such as those shown in FIG. 2. Contact is made .to the contactpads 51 by pressing engagement of the watch cover or by actuallysoldering the pads 51 to the corresponding pads within the interior ofthe aforementioned watch cover.

The cover plate 22 in this case is preferably the aforementioned siliconhaving the crystallographic configuration. As mentioned hereinbefore,when this silicon substance is etched with potassium hydroxide,truncated pyramid type apertures 30 are formed due to the preferentialetching of the silicon by the potassium hydroxide etching solution. Thefunction of the tapered sidewalls of these apertures will becomeapparent from iii consideration of two different types of light emittingdiodes.

The first of these light emitting diodes is a planar diffused diode andis shown in FIG. 4. This type diode configuration is typical of galliumarsenide phosphide diodes. As can be seen, the diode is composed of an Nand P type material with the junction shown by the dotted line 55. Theemission from the planar diffused diode is in the vertical direction, asshown by the arrows 59, when a voltage as shown by the battery 56 isapplied between the top contact 57 and the bottom contact 58. Thesearrows are perpendicular or within a small angle of the perpendicular tothe top surface of the diode shown in FIG. 4. Looking at the top of thediode then, the only portion of the diode which appears to be generatinglight is the interior portion shown by the P type material. This type ofdiode has obvious advantages in that the majority of the light ispropagated in a single direction.

A messa type diode is shown in FIG. 5. In this case the diode materialis red light emitting gallium phosphide having a N and P type region, asshown. Here the junction is shown by the line 61. When a potential isapplied across the junction by a battery shown at 62 across the contacts63 and 64, there is a nearly isotropic light emission in which lightemanates not only from the top surface, as shown by the arrow 66, butalso horizontally as shown by the arrows 67. It will be appreciated thata contact plate 68 reflects downwardly propagating light back throughthe diode in an upward direction.

Referring now to FIGS. 6, 7 and 8, if the diode is of the planardiffused type, such as that shown in FIG. 4, and if the cover isprovided with an inclined aperture shown in FIG. 6, then light emittedin a non-vertical direction will be reflected by the sidewalls 70 of theaperture 30 so as to redirect the light towards the user. The slope ofthe sidewalls both concentrates the light within a given viewing angleand permits the viewing of the light emitted by the light emitting diodefrom a position not directly above the diode. This gives the display ahigher intensity over a wider viewing angle. If the sidewalls 70 arevertical there is still a portion of the radiation from the diode whichis reflected back to the viewer, as can be seen in FIG. 7. It will beappreciated, however, that the viewing angle is narrowed significantlyby the user of perpendicular sidewalls of the apertures 30. The slantedor inclined sidewalls 70 have, however, particular advantage in anyelectro-optical display when used in conjunction with diodes havingeither nearly isotropic emissions or in which significant portions ofthe light are radiated laterally. Because of the nearly isotropic lightemission, a great deal of the light energy generated by the diode wouldbe lost unless the diode is located within the aperture 30 as shown inFIG. 8. Here the sidewalls redirect the light emanating-horizontallyfrom the diode and reflect it vertically. This type configurationenables the use of the low power gallium phosphide light emitting diodesbecause the majority of the radiation emitted by the diode is redirectedtowards the viewer.

Referring back now for a moment to FIG. 3, another feature whichcontributes to the enhancement of the contrast of the subject display inaddition to the particular aperture configuration just described, is theuse of filter material 75 at the base of these apertures. In the normalfabrication of light emitting diodes, the top surfaces of the diodes areusually coated with a quarterwave reflecting film so as to enhance theoutput of the diode. In addition to this type of quarter-wave filter, anarrow band-pass filter of a transparent material having the same coloras the output of the diode, is positioned between the diode and theobserver so that the contrast between the passive portion of the displayand the active portion of the display is increased. This contrastenhancement is accomplished because ambient light is absorbed by thefilter while light emanating from the light emitting diode istransmitted by the narrow band-pass characteristic. Thus, the ambientlight is in effect damped, while the light emitted from the lightemitting diode is enhanced. This, by definition, increases the contrastbetween the surface brightness of the light emitting diode and thesurface brightness of the area immediately surrounding the diode. Anytype material which is transparent to the light emitted by the diode maybe utilized. These materials include plastics and tinted glasses havingthe required transmission and absorption characteristics. The filter maybe placed as shown or may be placed on top of the cover plate so long asit does not cover the solar cells and the photodetector.

Another type filter can be utilized other than the narrow band-passfilter thus described. This type filter is a circularly polarizingfilter which circularly polarizes light passing therethrough. The effectof using circularly polarizing filter as the material 75 is as follows:Certainly the light emitted from the light emitting diode passes throughthe filter and has a circular polarization associated with it. Ambientlight, however, impinging on the timepiece base passes through theaperture 30 and through the filter 75 thereby acquiring a circularpolarization. The circularly polarized light then impinges on the topsurface of either the diode or the passive portion of the display suchthat it is phase shifted. When this light is reflected back to thefilter 75, it is attenuated in the filter because of this shift inpolarization. Thus ambient light is absorbed in the polarizing filterwhile the light emanating from the diode is not significantly absorbed.This enhances the contrast between the light emanating from the diodeand the light impinging on the display.

It will thus be appreciated that the inclined sidewall aperturestructure, alone or in combination with the aforementined filter,increases the contrast as defined above such that the power necessary tomaintain a given contrast is reduced. This in combination with thecontrol circuit described in connection with FIGS. 1 and 2, provide asystem for maximizing contrast in a timepiece light emitting diodedisplay while at the same time minimizing power consumption.

As shown in FIG. 9, the timepiece displayed need not be of theconcentric circular pattern shown in connection with FIGS. 1 and 3, butmay, in fact, be an alphanumeric display surrounded by rectangular solarcells 80, having a photodetector 81 somewhere on the face of thedisplay. Although more light emitting diodes are necessary in this typeof display than in the display hereinbefore described, it is possible tominimize the power consumption of the display shown in FIG. 9 in exactlythe same way as that shown in connection with FIGS. 1 and 3.

An alternate embodiment of the invention is shown in FIG. 10. In thisembodiment, as in the former embodiments, a series of light emittingdiodes 23 are mounted on a substrate 21. In this configuration, however,the cover plate is actually in toroidal form as shown by the referencecharacter 90. This cover is formed in generally by injection molding ofa plastic, which may either be an acrylic or a phenolic plastic having acolor imparted thereto corresponding to the color emitted by the lightemitting diodes therebeneath. The cover therefore serves both to protectthe light emitting diodes and as the aforementioned narrow band-passtype filter. It will be obvious that this cover should not besuperimposed either over the solar cells 35 or the photodetector 34 asit would absorb much of the energy conveyed by the light impinging onthe timepiece surface. The solar cells and the photodetector are mountedin a similar fashion to that shown in FIG. 1 on top of the substrate 21.In this case, however, the metallization interconnects between the solarcells and the control circuit 40, the photoconductor and the controlcircuit 00, are as shown, through the substrate 21. In this particularconfiguration, the control circuit is-attached directly to or embeddedin the substrate 21 and the logic circuit 25 mounted directly thereonwith the interconnections between the logic circuit and the controlcircuit being made at the control circuit-logic circuit interface. Theposition of the battery 41 is as shown so as to complete a compactpackage. The metallization which connects the logic circuit to thecathodes of the light emitting diodes is shown on the bottom surface ofthe substrate 21 with feed-throughs from the underneath surface of thesubstrate 211 to the top surface thereof and thence to the anodes of theindividual light emitting diodes. Further, a hemi-toroidal filter can beused on top of the structures shown at FIGS. l and 3 for filters 311 and75 respectively.

Referring to FIGS. 11 and 12, it can be seen that the output of thesolar cells is a monotonic function of the brightness of the ambient andthat the brightness of the output of the light emitting diodes is also amonotonic function of the current delivered thereto at a given voltage.These characteristics, as shown in FIGS. 11 and I2, enable theoutput ofthe solar cells to be applied in an increasing linear function to thelight emitting diodes as the ambient light increases.

The subject display can be fabricated in monolithic form as shown inFIGS. ll3a through lllii. In this configuration, a lightly doped siliconsdbstra'te 100 is etched so as to form the channels 99 as shown in FIG.13a. An epitaxial layer 101 of gallium phosphide is deposited over thetop surface of the silicon substrate 100 as shown in FIG. 13b.Thereafter, the structure shown in FIG. 13b is polished and the maskinglayer 103 consisting of dielectric material is deposited and patternedas shown in FIG. 1130. This mask covers the portions which are to becomethe solar cells, photodetectors, and light emitting diodes. Channels 102are etched in substrate I through the apertures in layer 103 as shown inFIG. 13d. These channels are deeper than channels 99 shown in FIG. 13ato provide positive isolation as will be described hereinafter. Afurther masking layer 105 of a dielectric material is deposited andpatterned as shown in FIG. Be. It will be appreciated that the maskinglayer I03 is conveniently removed from the top of substrate 100 prior tothe deposition of layer 105. The patterning oflayer 125 as shown in FIG.ll3e permits the formation of highly conductive areas 1100 by diffusionof suitable dopants which are of the same conductivity type as that ofthe substrate 100. AI-

ternately the central masking layer can be removed so that the centralarea 106 (the photodetector area), can also be provided with thediffusion 1104. Highly doped regions 104 are formed which eventually arenecessary to improve the conductivity of the large area solar cellsand/or the photodetector. These regions will eventually extend to thesurface of the solar cells. This is made possible by providing thatlayer H05 not extend up the sidewalls 118 of channels 102. It will beappreciated that because of the light doping of the silicon, a lightlydoped region 107 is formed centrally for the photodetector. The lightlydoped silicon also forms one of the junction elements for the solarcells as shown at regions I08. Regions 100, 104 and 108 are of the sameconductivity type.

The top surface of the structure thus formed in FIG. 13e is thenprovided with a further dielectric layer continuously across the topsurface. This is shown by the layer 110 in FIG. 13f. On top of thislayer is formed a poly-silicon layer 112 which is on the order of 3 to30 mils in thickness. As shown in FIG. 13f, the structure thus formed isthen lapped and polished to the line shown at 113 thereby forming aseries of dielectrically isolated islands containing portions of thesemiconductor devices to be completed therein.

Since channels 102 were etched deeper than channels 99 theaforementioned positive isolation is obtained because while lapping thesubstrate 100 to the line 113, channels 102 are penetrated before thegallium phosphide region 101 is reached. The resulting structure isshown inverted at FIG. 13g.

The light emitting diodes, solar cells and photodetector are thancompleted by diffusions through the top surface of the monolithicstructures shown in FIG. 13g. When fabricating the LEDs, solar cells,and photodetector it is necessary to deposit oxide and provide openingsfor the associated diffusions. This process requires several steps inthat different doping materials and/or concentrations are required tofabricate the parts. The resulting elements are shown in FIG. 13h.

As shown in this figure, starting from the left, a light emitting diodeis formed in the poly-silicon layer 112. The gallium phosphide material1101 which forms the light emitting diode is isolated by the layer 1110.This gallium phosphide layer is of a first conductivity type. Into thetop surface thereafter is formed a region 111 of a conductivity typeopposite to that of the material shown at 101. Next adjacent this diodeis a solar cell having a pot lined by the dielectric layer 1110. At thebottom of the solar cell is a deep diffused layer 104 which extends tothe surface of the monolithic device at the periphery of the solar cell.On top of the deep diffused layer is the lightly doped silicon region108 of a like conductivity type to that of the deep diffused layer. Aregion of an opposite conductivity type 121 isdiffused into region 108to complete the solar cell 125. In this embodiment the central element,the photodiode alsois surrounded by a dielectric isolation layer 110which is filled with the lightly doped silicon at region 107. Into thesilicon region 107 is diffused a material 131 of a type opposite to thatoff the silicon region 107 so as to complete the photodiode 130. It willbe appreciated that at this point the element 130 can be other than aphotodiode, in that it can be a phototransistor of a photoresistor.Thereafter, as shown in FIG. l3i, a further dielectric layer 132 isdeposited on the top surface and opened up over the active elements inthe light emitting diodes, the solar cells and the photodetector.Patterned metallization layers 134 are then formed on the top surfacethereof to complete the display. It will be appreciated that theparticular patterning utilized in metallizing each of the individualelements is dependent on the particular appearance that the display isto take on. In this case, no attempt is made to contact the individualelements through the poly-silicon substrate 112. Rather the contacts arerun to the edge of the substrate whereupon they are contacted byappropriate leads 140 disposed in a watch cover 145 which overlays thesecontacts.

Referring now to FIG. 14, the same structure as that shown in FIG. 1 isshown with the exception that no solar cells, photodetectors or powercontrol circuitry is shown. This configuration can be utilized inapplications in which power consumption is not a problem but in whichcontrast in the display must be enhanced by the apertures 30 and thenarrow band-pass filter 31. These applications include automobileclocks, the clocks powered by conventional house-power. In theseapplications the preferred embodiment has the aforementionedpreferentially etchable crystalline cover. Accordingly, in FIG. 15, thesame structure as that shown in FIG. is shown absent the photocells,photodetector and power control circuit. In this case, however, thelogic circuit 25 may be located on the top surface of the substrate21with the metallization 26 also running along the top surface.

Referring now to FIGS. 16 and 17, top views of the completed timepiecedisplay are shown, As mentioned previously, in order to represent thehour, minute and second a maximum of three diodes need be lit at onetime. The time is indicated first by the inner ring of diodes shown inFIG. 16 indicating the hour. The outer ring of diodes indicates minutesand seconds. The minute diode is activated substantially continuouslyfor 1 minute. During this time consecutive diodes are lit once eachsecond in a clockwise direction, as shown by arrow 145. As can be seenfrom FIG. 16, the time indicated by diodes 150, 151 and 152 is 1:12 and38 seconds. The two lightly shaded diodes 153 and 154 indicate those litin the preceding 2 seconds.

For convenience and to eliminate any ambiguity in the reading out of thetime from the display, half hour intervals are indicated as shown by the24 diode inner ring of FIG. 17. The time represented by diodes 160-163is 6:33 and 48 seconds. Diode 160 is lit to indicate that more than ahalf hour has elapsed. Prior to the half hour, only diode 161 is lit.This results in a display of the time of day with a maximum of fourdiodes.

Also shown in FIGS. 16 and 17 is the placement of four solar cells 35and the photodetector 34. Additionally, it will be obvious thatselective diodes may be made over-sized or a different color so as tofacilitate v the time read-out. Indeed the time readout may also befacilitated by appropriate markings on the display cover plate. A logiccircuit for driving the displays shown in FIGS. 16 and 17 is now brieflydescribed.

Referring now to FIG. 18, one possible logic 25 for driving the subjectdisplay is shown. The system operates from a crystal oscillator 240tuned to 2 Hz or 65,536 Hz. The output of the oscillator is a squarewave having this frequency which drives a countdown circuit 241. Thiscount-down circuit consists of a series of series-connected flip-flopsor divide-by-two" circuits. The output of the count-down circuit 241 isa 1 Hz square wave. The 1 Hz square wave drives three counters connectedin series. The first is the seconds" counter 242. For each incomingpulse there is an output in binary form indicating the number of thepulse from O to 59. The 60th pulse from the countdown circuit 241returns counters 242 to 0 and is transmitted to minutes counter 243. Theoutput of counter 243 is binary in form and indicates minutes from 0" to59. When the 60th minute occurs, counter 243 is reset and simultaneouslytransmits a pulse to the hours counter 244. The output of counter 244 isalso binary in form indicating one of 12 hours. In one embodimentcounters 242 and 243 are 6 flip-flop counters with counter 244containing only 4 flip-flops because only 12 diodes need be activated.Counters 242, 243 and 244, thus countdown the 1 Hz signal to providesignals representing minutes and hours. The outputs of counters 242-244are decoded by decoders 246-248. Decoders 246 and 247 take the binaryinformation from their respective counters and produce 60 individualsignals on 60 individual output lines 249 in timed sequence such thatonly one of the output lines 249 contains a signal 256 at any one time.The signals appearing in these output lines indicate respectivelyseconds and minutes. Decoder 248s output is 12 individual signals on 12different lines, likewise representing hours in timed sequence. Theoutput lines from the decoders are coupled to drivers 250-252. Thedrivers have 60,60 and 12 output lines 253 respectively. The presence ofa signal on an output line 253 from a decoder causes the power deliveredfrom the power control circuit 40 of FIG. 2 to be switched to acorresponding output line of the driver and thence to a correspondinglight emitting element. 255 connected as shown.

In order to utilize the time display as described above, one output fromtwo or more drivers is connected to a single light emitting element.Then as shown in FIG. 18, the element 255 is tied to the seconds and theminutes drivers. Likewise it will be obvious that a further half hourcounter-decoder-driver circuit could be provided having an outputcoupled in parallel with the output to driver 252 to a second set oflight emitting elements. Counters 242-244, decoders 246-248 and drivers250-252 are conventional.

If it is desired, a further power saving feature with the subjectconfiguration involves a partial intermittent readout to even furtherextend battery life. In this case, the photodector 37 and the powercontrol circuit 40 function as shown in FIG. 19 to turn off the lightemitting diode display below a given ambient lighting condition. Thiscondition is close to complete darkness which occurs under sleepingconditions at night or when the watch is worn under an opaque garmentsuch as the sleeve of a coat. Under dark conditions, the electroniccircuitry which produces signals indicating time is not interrupted.Only the power to the light emitting diodes is interrupted by shuttingdown the driver section or logic 25. However, a manually actuated switchis provided to over-ride the display shutdown if the user desires toread out the watch under these complete darkness conditions. This switchmay take the form of a mercury switch which is positioned so as to turnon the display when the watch is in the viewing position. This over-rideswitch is shown as switch 200 in FIG. 19. It willbe appreciated thatsince the power control circuit 40 can vary the power delivered to thelight emitting diode display, it can also interrupt the powercompletely. This is accomplished in the driver sections 250, 251i and252 as shown in H6. 118 by merely interrupting the power to the drivers.

in summary, there is disclosed both structural and electronic means forboth increasing the contrast in an electro-optical display while at thesame time decreasing the powernecessary to drive the display when theambient lighting condition is decreased or reduced. The electricalcontrol portion of the subject invention can be utilized independent ofthe structural contrast enhancing portions of the invention or incombination therewith. Likewise, the sturctural components can beutilized to advantage independently of the electrical control portions.Additionally, the power control portion of the invention may be utilizedindependently of the secondary power source purely as a contrast controlcircuit or may be used in combination with the solar cell configurationboth in a contrast control unit configuration and in a power boostingand battery charging configuration. Finally, a method has been describedin which the light emitting diodes, the solar cells and the ambientlight detector are fabricated in a single monolithic structure.

What is claimed is:

1. An electro-optical display for an electronic horologic instrumenthaving a light emitting diode readout and a primary self-containedportable source of electric power therewithin comprising in combination:

ambient light sensing means for detecting the amount of light falling onthe exposed surface of said display and for generating an electricsignal corresponding to the intensity of said light;

power regulating means operative in response to said electric signal forvarying the power available for energizing said light emitting diodes,the power varying function being such that a predetermined contrast ismaintained between the surface brightness of any excited light emittingdiode and the surface brightness of that portion of said exposedsurfaceimmediately adjacent said excited diode;

a secondary power source, said power regulating means distributing theadditional power available from said secondary powersource during highambient lighting conditions to portions of said horologic instrument inneed of said additional power whereby the display configuration, saidpower regulating means, and said secondary power source contributesignificantly to power conservation such that a prolonged substantiallycontinuous readout of said instrument is possible over an extensive timeperiod;

a support member, said light emitting diodes being mounted on saidsupport member and further including an opaque covering memberpositioned over said support member,

said covering member having apertures therethrough corresponding inlocation to the locations of said light emitting diodes, to redirect andintensify the output of said light emitting diodes over a given viewingangle, each of said apertures having inclined sidewalls, configured soas to flare outwardly thereby reflecting light from said light emittingdiodes at a viewing angle increased from that available by the use ofnon-inclined sidewalls having the same minimum aperture as said inclinedsidewalled aperture.

lid

2. The display as recited in claim l and further including narrowband-pass filtering means of said horologic instrument between saidlight emitting diodes and the user of said instrument for increasing thecontrast between said light emitting diodes and the face of saidinstrument immediately surrounding said diodes herein said filteringmeans is in the form of a hemi-toroidal cover and is of a materialabsorbent to all light except that generated by said light emittingdiodes, said material being of the same color as the light generated bysaid light emitting diodes and further including a circular substratewherein said light emitting diodes are arranged along the periphery ofsaid substrate, a central portion of said substrate being left free ofboth diodes and filtering means.

3. An electro-optical display for an electronic horologic instrumenthaving a primary self-contained portable source of electric powertherewithin comprising in combination:

a light emitting diode readout wherein said light emitting diodes arearranged .in concentric circles with diodes in one of said circlesrepresenting minutes and seconds, the diodes in another of said circlesrepresenting hours such that the time of day is read out from a maximumof three light emitting diodes, thus conserving on the number of diodesnecessary to represent the time of day and thus the power consumption ofthe horologic instrument;

ambient light sensing means for detecting the amount of light falling onthe exposed surface of said display and for generating an electricsignal corresponding to the intensityof said light;

power regulating means operative in response to said electric signal forvarying the power available for energizing said light emitting diodes,the power varying function being such that a predetermined contrast ismaintained between the surface brightness of any excited light emittingdiode and the surface brightness of that portion of said exposed surfaceimmediately adjacent said excited diode;

and a secondary power source, said power regulating means distributingthe additional power available from said secondary power source duringhigh ambient lighting conditions to portions of said horologicinstrument in need of said additional power whereby the displayconfiguration, said power regulating means, and said secondary powersource contribute significantly to power conservation such that aprolonged substantially continuous readout of said instrument ispossible over an extensive time period.

4. The display as recited in claim 1 wherein said covering member ismade from [1001 crystallographically oriented silicon and wherein saidapertures having inclined sidewalls are .formed by masking said coveringmember and etching all exposed areas with a potassium hydroxide etchingsolutio 5. The display as recited in claim 4 wherein the apertures insaid mask are square and the apertures in the covering member thusformed are in the form of truncated pyramids with the smaller portionadjacent to the top of said light emitting diodes.

6. The display as recited in claim it wherein said light emitting diodeshave significant emissions in directions non-perpendicular to the planeof said covering member and wherein said diodes are positioned withinsaid apertures when said covering member is in place such that emissionsnon-perpendicular to the plane of said covering member are redirectedtowards the user of said horologic instrument thereby decreasing theamount of power necessary in driving said last mentioned light emittingdiodes to obtain said predetermined contrast.

7. The display as recited in claim 1 wherein said secondary power sourceincludes solar cells mounted on top of said covering member and whereinsaid ambient light sensing means is also located on top of said coveringmember, whereby the output of said ambient light sensing means can becorrelated to the output of said solar cells in order to distribute thepower from said solar cells properly between said primary power sourceand said light emitting diodes.

8. The display as recited in claim 7 wherein said solar cells and saidambient light sensing means are embedded in said covering member andinsulated one from another.

9. The display as recited in claim 8 wherein said solar cells and saidlight sensing means are dielectrically isolated one from another in saidcovering member, said solar cells, said light sensing means and saidcovering member being formed monolithically.

10. The display as recited in claim 9 wherein said covering member issilicon.

11. The display as recited in claim 7 wherein all electrical componentsembedded within said covering member include metallization strips, saidmetallization strips being insulated from each other and running fromrespective electrical elements to the periphery of said covering member,whereby said metallization strips may be contacted at said periphery byconducting strips within an overlying portion of an outer casing forsaid horologic instrument thereby to connect electrical components onsaid covering member with components located underneath said coveringmember either underneath or on top of said support member.

12. The display as recited in claim 2 wherein said secondary powersource includes solar cells mounted on said substrate at said centralportion and wherein said ambient light sensing means is also located atsaid central portion.

13. The display as recited in claim 3 wherein additional light emittingdiodes in said hour indicating circle also indicates half hours.

14. The display as recited in claim 3 and further including anadditional circle of light emitting diodes indicating the half hour.

15. The display as recited in claim 3 and further including means forinactivating the diodes representing seconds by the user of theinstrument thereby preventing user fatigue or mesmerization in additionto decreasing power consumption.

16. Apparatus for improving the contrast between light emitting diodeshaving light emissions in more than one direction, mounted on asubstrate in'a horologic display and portions of said displaysurrounding said diodes comprising:

a cover plate for said display, said cover plate having aperturestherethrough over each light emitting diode, each of said apertureshaving inclined sidewalls tapered outwardly, said plate positioned suchthat each diode extends into a corresponding aperture a distancesufficient to provide that any exposed portion of the junction of eachdiode lies wholly within each aperture, said diodes being provided witha reflective backing plate such that any light generated by said diodesis redirected towards the user of said horologic display within apredetermined viewing angle.

17. The apparatus as recited in claim 16 wherein said cover plate ismade from crystallographically oriented silicon which has beenselectively etched by potassium hydroxide to form said apertures.

18. Apparatus for improving the contrast between light emitting diodesmounted so as to convey time in a horologic display and portions of saiddisplay surrounding said diodes comprising in combination:

a cover plate for said display, said cover plate having aperturestherethrough over each light emitting diode in the display, saidapertures having outwardly inclined sidewalls to permit a maximumviewing angle for said display, and

narrow band-pass filtering means located at the surface of said displaybetween said light emitting diodes and the user of said display, saidmeans acting so as to absorb light impinging on said display fromoutside sources, and so as to pass light generated by said diodeswhereby said contrast is improved by increasing the amount of diodegenerated light reaching said user while decreasing light reflected fromsaid display.

19. The apparatus as recited in claim 18 wherein said filtering means ismaterial which absorbs all light except that generated by said diodes,said material being of the same color as the light from said diodes.

20. The apparatus as recited in claim 18 wherein said filtering means ismaterial which circularly polarizes light therethrough such that whilethe light generated by said diode passes only once through said materialand is thereby circularly polarized, the light impinging on said displayfrom the outside thereof acquires a circular polarization when it firstpasses through said material, is phase shifted as it is reflected frominside said display and is attenuated as it passes back through saidmaterial as it passes therethrough a second time.

21. In combination:

a substrate,

light emitting diodes mounted on said substrate arranged to indicate thetime of day and electrically isolated one from another,

a logic circuit mounted on said substrate, said logic circuit generatingsignals in a timed sequence for activating selected light emittingdiodes to represent the time of day,

metallization connecting said light emitting diodes to said logiccircuit so as to energize said light emitting diodes in a sequencedetermined by said logic circuit,

a covering member over top said substrate, said covering member havinginclined sidewall apertures flaring outwardly from said substrate ateach of said light emitting diodes,

narrow band-pass filtering means at said covering member in position topass light generated by said diodes and to absorb light impinging on theexposed surface of said cover adjacent said diodes,

solar cells mounted on said cover, and

ambient light detecting means mounted on said cover, whereby saidcombination permits the formation of a horologic instrument in whichlight impinging on instrument aids in the powering of said instrumentand whereby said filtering means in

1. An electro-optical display for an electronic horologic instrumenthaving a light emitting diode readout and a primary self-containedportable source of electric power therewithin comprising in combination:ambient light sensing means for detecting the amount of light falling onthe exposed surface of said display and for generating an electricsignal corresponding to the intensity of said light; power regulatingmeans operative in response to said electric signal for varying thepower available for energizing said light emitting diodes, the powervarying function being such that a predetermined contrast is maintainedbetween the surface brightness of any excited light emitting diode andthe surface brightness of that portion of said exposed surfaceimmediately adjacent said excited diode; a secondary power source, saidpower regulating means distributing the additional power available fromsaid secondary power source during high ambient lighting conditions toportions of said horologic instrument in need of said additional powerwhereby the display configuration, said power regulating means, and saidsecondary power source contribute significantly to power conservationsuch that a prolonged substantially continuous readout of saidinstrument is possible over an extensive time period; a support member,said light emitting diodes being mounted on said support member andfurther including an opaque covering member positioned over said supportmember, said covering member having apertures therethrough correspondingin location to the locations of said light emitting diodes, to redirectand intensify the output of said light emitting diodes over a givenviewing angle, each of said apertures having inclined sidewalls,configured so as to flare outwardly thereby reflecting light from saidlight emitting diodes at a viewing angle increased from that availableby the use of non-inclined sidewalls having the same minimum aperture assaid inclined sidewalled aperture.
 2. The display as recited in claim 1and further including narrow band-pass filtering means of said horologicinstrument between said light emitting diodes and the user of saidinstrument for increasing the contrast between said light emittingdiodes and the face of said instrument immediately surrounding saiddiodes herein said filtering means is in the form of a hemi-toroidalcover and is of a material absorbent to all light except that generatedby said light emitting diodes, said material being of the same color asthe light generated by said light emitting diodes and further includinga circular substrate wherein said light emitting diodes are arrangedalong the periphery of said substrate, a central portion of saidsubstrate being left free of both diodes and filtering means.
 3. Anelectro-optical display for an electronic horologic instrument having aprimary self-contained portable source of electric power therewithincomprising in combination: a light emitting diode readout wherein saidlight emitting diodes are arranged in concentric circles with diodes inone of said circles representing minutes and seconds, the diodes inanother of said Circles representing hours such that the time of day isread out from a maximum of three light emitting diodes, thus conservingon the number of diodes necessary to represent the time of day and thusthe power consumption of the horologic instrument; ambient light sensingmeans for detecting the amount of light falling on the exposed surfaceof said display and for generating an electric signal corresponding tothe intensity of said light; power regulating means operative inresponse to said electric signal for varying the power available forenergizing said light emitting diodes, the power varying function beingsuch that a predetermined contrast is maintained between the surfacebrightness of any excited light emitting diode and the surfacebrightness of that portion of said exposed surface immediately adjacentsaid excited diode; and a secondary power source, said power regulatingmeans distributing the additional power available from said secondarypower source during high ambient lighting conditions to portions of saidhorologic instrument in need of said additional power whereby thedisplay configuration, said power regulating means, and said secondarypower source contribute significantly to power conservation such that aprolonged substantially continuous readout of said instrument ispossible over an extensive time period.
 4. The display as recited inclaim 1 wherein said covering member is made from (100)crystallographically oriented silicon and wherein said apertures havinginclined sidewalls are formed by masking said covering member andetching all exposed areas with a potassium hydroxide etching solution.5. The display as recited in claim 4 wherein the apertures in said maskare square and the apertures in the covering member thus formed are inthe form of truncated pyramids with the smaller portion adjacent to thetop of said light emitting diodes.
 6. The display as recited in claim 1wherein said light emitting diodes have significant emissions indirections non-perpendicular to the plane of said covering member andwherein said diodes are positioned within said apertures when saidcovering member is in place such that emissions non-perpendicular to theplane of said covering member are redirected towards the user of saidhorologic instrument thereby decreasing the amount of power necessary indriving said last mentioned light emitting diodes to obtain saidpredetermined contrast.
 7. The display as recited in claim 1 whereinsaid secondary power source includes solar cells mounted on top of saidcovering member and wherein said ambient light sensing means is alsolocated on top of said covering member, whereby the output of saidambient light sensing means can be correlated to the output of saidsolar cells in order to distribute the power from said solar cellsproperly between said primary power source and said light emittingdiodes.
 8. The display as recited in claim 7 wherein said solar cellsand said ambient light sensing means are embedded in said coveringmember and insulated one from another.
 9. The display as recited inclaim 8 wherein said solar cells and said light sensing means aredielectrically isolated one from another in said covering member, saidsolar cells, said light sensing means and said covering member beingformed monolithically.
 10. The display as recited in claim 9 whereinsaid covering member is silicon.
 11. The display as recited in claim 7wherein all electrical components embedded within said covering memberinclude metallization strips, said metallization strips being insulatedfrom each other and running from respective electrical elements to theperiphery of said covering member, whereby said metallization strips maybe contacted at said periphery by conducting strips within an overlyingportion of an outer casing for said horologic instrument thereby toconnect electrical components on said covering member with componentslocated underneath said covering member either underneath or on top ofsaid support member.
 12. The display as recited in claim 2 wherein saidsecondary power source includes solar cells mounted on said substrate atsaid central portion and wherein said ambient light sensing means isalso located at said central portion.
 13. The display as recited inclaim 3 wherein additional light emitting diodes in said hour indicatingcircle also indicates half hours.
 14. The display as recited in claim 3and further including an additional circle of light emitting diodesindicating the half hour.
 15. The display as recited in claim 3 andfurther including means for inactivating the diodes representing secondsby the user of the instrument thereby preventing user fatigue ormesmerization in addition to decreasing power consumption.
 16. Apparatusfor improving the contrast between light emitting diodes having lightemissions in more than one direction, mounted on a substrate in ahorologic display and portions of said display surrounding said diodescomprising: a cover plate for said display, said cover plate havingapertures therethrough over each light emitting diode, each of saidapertures having inclined sidewalls tapered outwardly, said platepositioned such that each diode extends into a corresponding aperture adistance sufficient to provide that any exposed portion of the junctionof each diode lies wholly within each aperture, said diodes beingprovided with a reflective backing plate such that any light generatedby said diodes is redirected towards the user of said horologic displaywithin a predetermined viewing angle.
 17. The apparatus as recited inclaim 16 wherein said cover plate is made from (100)crystallographically oriented silicon which has been selectively etchedby potassium hydroxide to form said apertures.
 18. Apparatus forimproving the contrast between light emitting diodes mounted so as toconvey time in a horologic display and portions of said displaysurrounding said diodes comprising in combination: a cover plate forsaid display, said cover plate having apertures therethrough over eachlight emitting diode in the display, said apertures having outwardlyinclined sidewalls to permit a maximum viewing angle for said display,and narrow band-pass filtering means located at the surface of saiddisplay between said light emitting diodes and the user of said display,said means acting so as to absorb light impinging on said display fromoutside sources, and so as to pass light generated by said diodeswhereby said contrast is improved by increasing the amount of diodegenerated light reaching said user while decreasing light reflected fromsaid display.
 19. The apparatus as recited in claim 18 wherein saidfiltering means is material which absorbs all light except thatgenerated by said diodes, said material being of the same color as thelight from said diodes.
 20. The apparatus as recited in claim 18 whereinsaid filtering means is material which circularly polarizes lighttherethrough such that while the light generated by said diode passesonly once through said material and is thereby circularly polarized, thelight impinging on said display from the outside thereof acquires acircular polarization when it first passes through said material, isphase shifted as it is reflected from inside said display and isattenuated as it passes back through said material as it passestherethrough a second time.
 21. In combination: a substrate, lightemitting diodes mounted on said substrate arranged to indicate the timeof day and electrically isolated one from another, a logic circuitmounted on said substrate, said logic circuit generating signals in atimed sequence for activating selected light emitting diodes torepresent the time of day, metallization connecting said light emittingdiodes to said logic circuit so as to energize said light emittingdiodes in a sequence determined by said logic circuit, a covering memBerover top said substrate, said covering member having inclined sidewallapertures flaring outwardly from said substrate at each of said lightemitting diodes, narrow band-pass filtering means at said coveringmember in position to pass light generated by said diodes and to absorblight impinging on the exposed surface of said cover adjacent saiddiodes, solar cells mounted on said cover, and ambient light detectingmeans mounted on said cover, whereby said combination permits theformation of a horologic instrument in which light impinging oninstrument aids in the powering of said instrument and whereby saidfiltering means in combination with said inclined sidewall aperturesincreases the contrast between light generated by said diodes and lightreflected from the exposed portions of said horologic instrument suchthat a portable battery powered timepiece is made feasible.
 22. Thecombination as recited in claim 21 wherein said substrate is selectedfrom the group of materials consisting of: semiconductors, plastics,ceramics and glasses.
 23. The combination as recited in claim 22 whereinsaid covering member is made from an anisotropically etchablecrystalline material, said inclined sidewalled apertures being formed byetching said crystalline material with an anisotropic etchant.
 24. Thecombination as recited in claim 21 and further including metallizationon said covering member running from said diodes, said solar cells andsaid ambient light detecting means to the periphery thereof, and ahousing member overlying said periphery, said housing member includingmeans for contacting various portions of said metallization at saidperiphery and for connecting said portions to points interior to saidhousing member.
 25. The combination as recited in claim 21 wherein saidlight emitting diodes and said logic circuit are formed in saidsubstrate and said solar cells and said ambient light detecting meansare formed in said covering member.
 26. The combination as recited inclaim 21 wherein said solar cells and said ambient light detecting meansare embedded in said covering member and dielectrically isolated onefrom another.
 27. The combination as recited in claim 50 whereinembedding includes epitaxial deposition and diffusion techniques.